1. Technical Field
The present disclosure relates to an active probe pod used in a logic analyzer, in particular, to an active probe pod capable of capturing a weak signal input from a DUT circuit board and transmitting such over a shortened signal transmission path, minimizing the occurrence of the signal reflection, ensuring the signal quality, and avoid the attenuation of the signal.
2. Description of Related Art
In the current digital era, the traditional oscilloscope has been proved unable to measure logic signals in 8-16 and even more channels. Despite the in-circuit emulator (ICE) could help resolve some relevant problems, the software development-oriented ICE could be having hard time handling the actual time sequence-related issues. Plus, considering the ICE could only be exclusively used in certain microcomputer systems the logic analyzer still entrenches as one of the necessary equipments for digital engineers. The logic analyzer could have data illustrated in an organized or structured fashion when displaying the operations of the digital circuitry.
The traditional logic analyzer utilizes a passive probe pod in which signal detection circuitry has been incorporated. When the total capacitance of each channel may be at 16 pF, up to eight channels may be detected at the same time. A passive probe pod 2 shown in FIG. 1A could be a single-end wire and is configured to capture the weak signal input from a DUT circuit board 1 before transmitting the captured weak signal input over a long-distance signal transmission path to an operational amplifier 31, a comparator 32, and an FPGA decoder 33, all of which are disposed inside a logic analyzer 3. The operational amplifier 31 could pre-amplify the weak signal input received by the logic analyzer 3 and the comparator 32 could thereafter output a LVDS differential signal to the FPGA decoder 33 where the decoding of the same is performed.
However, as shown in FIG. 1B the traditional approach could be associated with the following disadvantages:                (1) the weak signal input inevitably would be attenuated after the long-distance transmission over the single-end wire, negatively affecting the signal quality, which in turn undermines the subsequent amplification and the decoding (for example, no data could be decoded or the data loss); and        (2) the signal reflection could occur after the long-distance signal transmission for the weak signal input over the single-end wire, also subjecting the amplification and the decoding to the data loss or lack of the data to be decoded.        
Accordingly, in order to overcome the above problems it is wise to properly set up the signal transmission path for the weak signal input so that the weak signal is not transmitted over the long-distance transmission path. Further, the weak signal input could be converted into the corresponding differential signal, which may be more suitable for the long-distance transmission, since the differential signal is less susceptible to the interference.